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Using biological control strategies for turf, Part 2: Diseases

Eric B. Nelson, Cornell University

Turfgrass managers increasingly view biological control as a desirable
alternative treatment because it can be a rational way to extend and
augment the efficacy of fungicides and, at the same time, reduce the
overall environmental load of pesticides. Most importantly, however,
biological control is an effective, sustainable solution for maintaining
turfgrass health.

The most common biological-control strategies involve either applying
microbial inoculants or using organic amendments to encourage the
activities of native pathogen-suppressive microorganisms. The goal with
both of these strategies is to increase the populations and activity of
disease-suppressive microbes associated with turfgrass plants.

Bioaugmentation with microbial inoculants
Researchers have studied numerous microbial inoculants over the past
decade-especially species of the bacteria Pseudomonas, Bacillus,
Enterobacter, Streptomyces and the fungus Trichoderma-for control of
several diseases, including brown patch, dollar spot, Pythium blight and
root rot, summer patch, take-all patch, leaf spots and Typhula blight. Many
inoculants still are in development, though two are available, and a few
more could reach the market place in the next year or two.

* Maintaining populations. One of the more difficult obstacles to the
successful use of microbial inoculants has been their inconsistent
performance in the field. Many examples exist where biological control is
as effective as fungicide applications in laboratory tests but inconsistent
and unpredictable in field tests. Although we do not understand all the
factors that contribute to variability in performance, it may be due do to
variables influencing population level, activity and survival. For example,
environmental factors such as temperature, moisture and ultraviolet light
change dramatically within a turfgrass canopy, perhaps in ways detrimental
to microbial growth and activity. Further, management practices such as
grooming, irrigating, fertilizing and applying pest controls may also
influence microbial growth and activity.

One of the primary factors contributing to reduced efficacy in the field is
the failure to maintain adequate populations of the microbes in turfgrass
soils. Numerous laboratory experiments show that populations of biocontrol
organisms must stay at high levels (usually greater than 1 million cells
per gram of soil). If populations drop below this level, control efficacy
is in jeopardy. To overcome this, one or more things must happen:
*Applications must be frequent
*Applications must occur at times when environmental conditions strongly
favor activity of the inoculant
* The inoculant must be formulated in a way that favors its activity and
survival.

Some people question the sustainability and environmental impacts of
frequent applications of high levels of microbial inoculants. Nevertheless,
frequent application of inoculants may provide the only effective approach
for suppressing foliar diseases and maintaining populations on foliage,
because this habitat is generally more unfavorable for microbial
persistence than a soil environment. Selection of inoculants adapted
specifically to the turfgrass environment may facilitate their activity and
the maintenance of stable populations.

In addition to maintaining populations of introduced inoculants,
application timing is also critical. Recent studies with various microbial
inoculants show that applications made after sundown result in superior
control compared to applications made during the daytime hours. Further,
applications made on a daily basis generally result in more effective
control than applications made on a weekly basis. Recent studies also
suggest that for the most effective control with microbial inoculants, the
volume of water with which you apply inoculants must be greater than 2
gallons per 1,000 square feet (rates similar to conventional fungicide
applications).

Researchers must improve their understanding of these factors to develop
better application techniques and formulations to increase performance
consistency. From the turf manager's perspective, it's equally important to
provide the agronomic conditions that favor turfgrass growth and
development, because these are the same conditions that tend to promote
biological control.

BioJect actually ferments TX-1 on-site and is part of the package approved
by EPA. John Doyle, vice president of Eco Soil, explains, "What is unique
about this approval is that this is the first time EPA has approved a
biopesticide delivered in a method of on-site fermentation. In this case,
BioJect ferments and dispenses biologicals through the irrigation system."

Key to approval was ensuring that BioJect posed no significant risk of
applying some harmful microbe through the system. "What we documented to
the EPA was essentially that what we put into the BioJect system is exactly
what was coming out, via the irrigation system," says David Odelsen, vice
president of research and development. "Specifically, we documented that
when [TX-1] is inoculated and fermented (as an active ingredient) in a
bioreactor system, TX-1 is the only organism that was produced and
subsequently distributed through the system," Odelsen states. Eco Soil will
lease the BioJect system to golf courses and provide maintenance and
upgrades through Turf Partners Inc.

EPA granted approval after university research demonstrated that TX-1 is
non-pathogenic to humans, plants and animals. It controls Anthracnose,
dollar spot, Pythium, leaf spot, take-all patch, fairy ring, pink patch,
gray leaf spot, Microdochium patch, summer patch and necrotic ring spot.
TX-1 does not control diseases in the manner of traditional fungicides and
does not entirely eliminate the need for them. However, it does provide
significant suppression of the listed diseases. Therefore, it can extend
spray intervals considerably or eliminate applications altogether by
reducing disease activity below typical treatment thresholds.

TX-1 bacteria provide control by secreting phenazine carboxylic acid (PCA),
a compound with significant anti-fungal properties. For ongoing control,
frequent applications are necessary to maintain high population levels of
the bacteria. The BioJect irrigation-injection system is a practical method
of doing so, and its on-site production (fermentation) of TX-1 eliminates
the shipping and storage problems inherent in using biological products.

Biostimulation with compost amendments
Unlike microbial inoculants, the goal with compost amendments is to enhance
the native populations of soil organisms. People have used composts in soil
management for centuries and it has been an effective and sustainable means
of improving productivity and overall plant health. Over the past 10 or 15
years, studies have clearly demonstrated the potential for composts to
reduce the severity and incidence of many turfgrass diseases. For example,
monthly topdressing applications of composts at rates as low as 10 pounds
per 1,000 square feet are effective in suppressing diseases such as dollar
spot, brown patch, Pythium root rot, Pythium blight, necrotic ringspot, red
thread and Typhula blight. Levels of disease control can vary from 0 to 94
percent, depending on the target disease, the type of compost and the
manner and degree to which the material is composted.

Root-zone compost amendments have the potential to provide much higher and
longer-lasting disease suppression of root-infecting pathogens than do
topdressing amendments. Studies have shown that amending sand-based greens
with municipal-biosolids compost, brewery-sludge compost or an uncomposted
reed-sedge peat induces a high level of suppression of Pythium root rot.
These amendments have provided complete control for 6 months after
incorporation and retained disease-suppressive properties for up to 4 years.

Composts affect diseases largely because of their impacts on soil
microorganisms but also because of the microorganisms they contain.
Suppressive composts generally are higher in microbial activity than
non-suppressive composts. Usually, immature (1 to 3 months) composts that
are still in an active state of decomposition are low in microbial activity
and not disease-suppressive. However, when allowed to age for a suitable
period (2 to 3 years), many composts become highly suppressive.

Biological-control products for turfgrass
Today, turfgrass managers have numerous products available for managing
diseases. The numbers and types of organic amendments and microbial
inoculants currently on the market for disease control in turfgrasses are
overwhelming. In many cases, it is difficult to know which of these
products you should take seriously. I group biological-control products
currently available to the turfgrass industry into four different classes:
*EPA-registered inoculants
*Unregistered inoculants for which documented levels of disease reduction
are claimed
*Unregistered inoculants for which disease reduction claims have not been
validated
* Products that suppress diseases but are marketed for other purposes. Such
products include natural organic fertilizers and compost amendments,
whereas many of the microbial inoculants fall into the first three
categories.

The first class of products is registered in the same manner as chemical
fungicides. Currently, Wilbur-Ellis' BioTrek 22G, a preparation of
Trichoderma harzianum, is one of only two microbial-based fungicides
registered for use on turfgrasses in the United States. The other is Eco
Soil Systems' TX-1, a Pseudomonas aureofaciens strain which received
federal registration in February (see "TX-1 receives registration," page
XX).

Manufacturers do not have the right to make claims about the control of
specific diseases without EPA registration as a biological fungicide.
Products not registered with the EPA for turfgrass use-but with labels that
claim control of specific diseases-cannot legally be sold or used for
turfgrass applications. Nevertheless, many of these types of products are
currently available to turfgrass managers. Some are registered on other
crops but currently lack a turfgrass registration. Although EPA does not
require efficacy data for registration, many states demand it before
granting registration in that state. The registration process, therefore,
ensures that manufacturers have conducted some efficacy testing of the
product.

The second class of products is one of the more difficult groups to assess.
Suppliers market these unregistered products, at least in part, for disease
control. Although their labels do not normally list specific diseases, the
wording frequently infers that the product will non-specifically reduce the
incidence or severity of turfgrass diseases. By making such claims,
regardless of how vague they may be, such products require EPA registration
for legal use. Strictly speaking, then, their sale and use for disease
control in turfgrass is a violation of the law both on the part of
applicators and the suppliers that market them for disease control.
Nevertheless, dozens of these products are available to golf-course
superintendents, with many new ones appearing every year.

The third class of products includes a large group of biologically based
materials sold for a variety of turfgrass ailments, including disease
control. In many cases, the manufacturers have used little or no logic in
the selection of the particular "active" microbial strains in the product
and no logical development of appropriate application strategies. Although
it is difficult to know how much testing has gone into the development of
these products, it is doubtful that most manufacturers have ever
scientifically tested them on turf for disease-control efficacy. These
products rely primarily on shrewd marketing and testimonials to support
sales. It is this group of products that poses the greatest risk to the
future of biological control in turfgrasses. Failures with these products
can instill deep-seated skepticism among turfgrass managers, making them
reluctant to use any such products, including those whose manufacturers
have taken the steps necessary to obtain efficacy data and EPA registration.

The fourth group of products includes a variety of natural-organic
fertilizers, root enhancers, soil inoculants and organic amendments. Many
of these materials have been available to the turfgrass industry for years.
Most are not marketed for disease control but may have some disease-control
efficacy. In some cases, these products may be well-tested, whereas others
have no documented efficacy. Although some of these products may have a
high degree of quality control for their fertility content, the
manufacturers provide little or no quality control over disease-suppressive
properties.

The future of biological disease control in turf
Turfgrass management is entering an age where turf managers are seeking
microbiological solutions for biological problems. It is increasingly
apparent that maintaining active microbial communities in turfgrass soils
is a vital part of overall turfgrass health. Studies on biological control
clearly show the potential to affect disease control through both of the
microbial-based technologies I've described. Currently, we have more
questions than answers about how to optimize these technologies.
Nevertheless, interest in the development and commercialization of
biological-control products continues to grow. Sound, biological-based
approaches to turfgrass management will provide additional tools for
maintaining a sustainable, healthy turfgrass ecosystem.